According to the webcast streaming technology, a client-server connection is established, where the server transmits multiple streams or files to each client. Each stream or file relates to a different point of view. Each stream or file is output either from stored files or from live encoded feeds, for example by means of encoding stations.
FIG. 1 shows an exemplary embodiment of such prior art system. Products embodying such technology are, for example, produced by the company iMove Inc., and shown at the website address http://www.imoveinc.com. A streaming server 1 located on the server side receives audio-visual information from a number of different audio-visual files or streams connected to the source of information, such as an audio file FA and video files FV1 . . . FVn, all indicated with 2 in the Figure.
The audio-visual content of the number n of files 2 (three in the example) is streamed from the server to the client over a connection 3. The connection 3 is an Internet connection. As a consequence, it can assemble different network technologies, such as Ethernet, Frame Relay, ATM switch, CDN, satellite uplink and downlink, DS1, D2, DS3 (or the corresponding European E1, E2, E3), fiber, modem, ISDN, xDSL, and so on. All these technologies use the IP protocol and are interconnected by routers, bridges and gateways. Assuming that the maximum available bandwidth for the connection is b, the maximum bandwidth for each streamed file will be b/3.
On the client side, a streaming client 4 software provides for the interpretation of the received streams. One of the streams is shown on the screen of the client in a current view. For example, the contents relating to the video file FV2 can be shown, as indicated by the box 5, represented in solid lines and relating to the “current view (2)”, namely the view relating to the contents of FV2.
As soon as the viewer wants to switch on a different point of view, he will send a command to the GUI (graphic user interface) 6, for example by means of a pointing device (not shown in the Figure), and from the GUI 6 to the streaming client 4. As a result, the audio-visual content shown on the screen will from now on relate for example to the contents of FV1, indicated by the streaming server 7 box, represented in dotted lines.
A problem of the prior art shown in FIG. 1 is that the required bandwidth is directly proportional to the number of cameras (different points of view) adopted. Therefore, a high bandwidth is required in order to obtain an audio-visual content of a good quality.
In order to solve such problem, a different session for each view could be established. This means that only a single audio-visual content at the time would be streamed and, each time a client desires to switch from one view to another, the streaming server 1 would pick a different file and retransmit it to the client. Such technology is, for example, adopted in the “BigBrother” series, when transmitted over the Internet. See, for example, http://www.endemol.com or http://www.cbs.com/primetime/bigbrother. While this solution allows a larger bandwidth, the switching delay is unacceptable for the user. In fact, according to the usual way of streaming signals, a first step of the streaming process is that of buffering data on the client computer. Then, after a predetermined amount of time, the data are shown on the screen of the client while, at the same time, the remaining data are being transferred over the connection. This means that, each time a switching occurs, a considerable amount of time would be spent in buffering again the audio-visual data of the following stream, with a delay which would be unacceptable for most kind of commercial applications and which would result in an interruption of both the audio and the visual content of the signal transmitted on the screen.